1. Field of the Invention
The present invention relates to a heating unit of a vehicle heating system. More particularly, the present invention relates to a heating unit for heating blowing air at a low power consumption rate by arranging microwave absorbing/heat emitting members that absorb microwaves and emit heat in a vehicle air conditioning unit or in a vehicle air duct.
2. Prior Art
Various hybrid vehicles and electric vehicles have been proposed and developed for the purpose of improving the fuel efficiency of vehicles and reducing the quantity of CO2 gas emissions from vehicles in recent years. Such vehicles, electric vehicles in particular, are equipped with an electric motor that is operated by electric power supplied from the battery mounted in the vehicle when driving the vehicle by means of the electric motor. Then, electric power is consumed at a high rate to give rise to a problem of a short cruising distance. The cruising distance can be increased by raising the capacity of the battery mounted in the vehicle. However, the vehicle weight will be raised accordingly to by turn lower the power consumption efficiency and reduce the cruising distance of the vehicle. Therefore, the battery needs to be charged frequently.
Thus, in hybrid vehicles and electric vehicles, the electric power consumption rate of other than the electric equipment for driving the vehicle and securing the safety of the running vehicle needs to be minimized. For instance, Patent Document 1 proposes a vehicle air conditioning system that is operated by using a technique developed for reducing the power consumption rate of a vehicle air conditioning system.
A vehicle air conditioning system as illustrated in Patent Document 1 employs a PTC heater (positive temperature coefficient heater) formed by arranging a large number of PTC thermistors as heating members in a vehicle air conditioning unit and the system includes an excess power data acquisition means for determining the excess power in a vehicle that can be supplied to a PTC heater and a power consumption data acquisition means for determining the power consumption rate of the FTC heater that changes as a function of the temperature of the PTC thermistors. The power consumption rate of the vehicle in a heating operation is reduced by controlling the PTC thermistors on the basis of the excess power as determined by the excess power acquisition means and the power consumption rate as determined by the power consumption data acquisition means.
A PTC heater is a heater having a characteristic that its power consumption rate is reduced as its temperature rises but it is accompanied by a problem of consuming power at a high rate in a situation where the air conditioning temperature of the vehicle in which it is mounted and hence the temperature of the PTC heater itself is not high. Such a situation can be observed when the ambient temperature is low or when the vehicle is in the initial stages of a running operation. Particularly, when such a PTC heater is mounted in an electric vehicle, all the energy for driving the vehicle to run depends on one or more batteries so that, as the power consumption rate of the vehicle air conditioning system rises, the running distance of the vehicle is reduced and hence the battery charging cycle of the vehicle becomes short.